The present invention relates to an asphalt paving screed, and in particular, an extendable asphalt paving screed.
Floating screed pavers are well known in the art and typically include a paving vehicle with a reservoir of asphalt material and a main screed which trails behind the paving vehicle to spread out, level, and compact the asphalt paving material. The main screed is connected to the paving vehicle by pivoted towing arms to permit the screed to "float" over the surface on which asphalt is to be applied.
In order to widen the asphalt paving path, prior art devices have provided extendable screeds which can extend laterally outward from a main screed. Extendable screeds typically include means for selectively sloping the extendible screed relative to the main screed to form a sloped shoulder on the paved surface. North American-type prior art extender screeds accomplish this sloping by rotatably mounting the extender screed relative to the main screed. For example, U.S. Pat. No. 5,230,642 to Heeler, et al. discloses an extendable screed with a means for pivoting the extender screed relative to the main screed.
A common problem plaguing many extendible screeds includes deflection and/or misalignment of the extender screed relative to the main screed due to the force of the asphalt paving material pushing against the front of the extender screed as the main screed and extender screed are pulled along by the paving vehicle. Deflection or misalignment of the extender screed relative to the main screed can result in an uneven, low quality paved road surface.
North American-type prior art extender screed arrangements include extension mechanisms (an assembly to permit an extender screed to extend laterally outward from a main screed) that are not symmetrical as they overlap laterally to permit full retraction of the extender screeds relative to the main screed. This non-symmetrical overlap causes each screed of the pair of extender screeds to have a different deflection characteristic during paving since slightly different framing of the extender screed and extender mechanism framing is required to permit the overlap necessary for full retraction of the extender mechanisms.
While prior art European-type extendible screeds typically are symmetrical, these screeds are bulkier having multiple vertical actuators to control height adjustment and sloping of the extender screeds. The actuators are commonly positioned at opposite ends of the extender screed (e.g. at the inboard end and outboard end). The actuators positioned at the outboard end of the extender screed contribute to undesirable deflection of the extender screeds since the outboard actuators and related structure add weight at a point furthest away from the main screed. In addition, adjusting the slope of the extender screed to cause a slope in the paved surface is cumbersome since the vertical actuators are spaced apart at opposite ends (e.g. inboard and outboard ends) of the extender screed. Moreover, this large spacing between the vertical actuators results in an inability to quickly change the slope of the extender screed, as is more commonly required in North American-type paving projects. Finally, the European-type extender screeds also are commonly linked to the main screed via a pair of upper and lower links arranged on top of the extender screed and extending the entire width of the extender screed. These upper and lower links add weight and bulk to the extender screeds, particularly at the outboard end of the extender screed, thereby further contributing to undesirable deflection of the extender screed relative to the main screed.
Accordingly, prior art extendible asphalt paving screeds can still be improved by further minimizing deflection of the extender screed relative to the main screed during asphalt paving while still permitting quick and precise vertical adjustment and sloping of the extender screed relative to the main screed.